Audio selective fading system



Feb. 6, 1962 w. D. ALDRIDGE, JR 3,020,343

AUDIO SELEGTIVE FADING SYSTEM Filed March 29, 1960 In; MII' a Bf @waa/@ hired erases This invention relates to audio selective fading systems. More particularly, the present invention relates to sound systems having selective audio sources sequentially switched into output transmission with fading in and out of at least one of the audio sources.

In many public address systems, it has been found desirable to provide music over the system between vocal public announcements. The music provides a pleasing background at places of work or at places `of entertainment, such as at race tracks or stadiums. In order to achieve a pleasant break between the music and the vocal announcement, it has beenv found desirable to slowly turn down the volume of the music system by manually operating the conventional potentiometer type control switch of either the input from a phonograph or the output of the amplifier. In this manner the music is faded out and a microphone switch may then be activated to bring the microphone into operation so that the public announcement may be made. At the conclusion of which, the microphone is turned off and the music amplifier system is slowly brought into play by manually turning up the volume. 4It has 'been found to be entirely undesirable to merely employ a simple throw switch which cuts in and out the music at normal volume without attempting a fading in and out control.

Accordingly, it is a primary object of the present invention to provide a new and improved system having automatic fading means for selectively tapping audio sources for emanation over a sound transmission system.

lt is another object of the present invention to provide a new and improved system having automatic fading means for selectively tapping either a music sound source or a vocal announcement source for emanation over a sound transmission system.

-It yis yet another object of the present invention to provide a new and improved sound system having an ingenious circuitry for fading out one audio source as another audio source is brought into alignment.

These together with other objects and Iadvantages which will become subsequently apparent reside in the details of construction and operation as more fully hereinafter described and claimed, reference being had to the accompanying drawing forming a part hereof, wherein like numerals refer to like parts throughout, and in which:

The FIGURE relates to the circuitry applicable in a diagrammatic manner.

Referring to the drawing, a music source, such as a phonograph (not shown), has its input at 11. It will be observed that the electronic components above the dashed line A-A depicts a conventional amplitier with a mixer tube. The volume of the phonograph input is controlled by variable resistance 12, through a tap lead which is capacitance coupled through condenser 13 to grid 14 of mixer tube 15. The anode 1e of the mixer tube 15 is capacitance coupled through condenser 17 to a driver stage. A suitable supply of B plus voltage is tapped into the line through resistance 17A. When the music is to be broadcast over the sound system, switch 18, associated with microphone 19, is maintained in a closed position. Microphone 19 is connected to the `operating electronic components containing chassis by a three wire shielded cable 20 and is plugged into the chassis by suitable plug and socket arrangement 2f.. When switch 13 is closed, lead 22 provides electrical energy to relay 23 which is grounded at 24. A resistance 25 in the line -acts as a 3,020,343 Patented Feb. 6, 1952 lter to avoid audible switch click. Relay 23 operates a double pole switch having arms 2.5 and 27. When relay 23 is energized the microphone through lead 28 by means of contact 29 is grounded at 30. At the same time, the energy level at contact 31 and lead 32 is at ground. It will be appreciated that the position of switch 1S and relay switch arms 26 and 27 prevent the operation of the microphone, but does not prevent the operation of the input voltage from the music source.

When switch 18 is opened, the microphone 19 becomes unshorted because relay 23 is cle-energized so that suitable resilient means urges arms 26 land 27 to contacts 33 and 34, respectively. Removal of `arm 27 from contact 29 u-nshorts the microphone. At the same time, arm 26 is permitted to make connection with contact 33, thereby energizing indicator light 35 through suitable voltage rel duction means. Removal of arm 26 from contact 31 unshorts the 30 volts of negative bias voltage for the music fader circuit at 36 which is fed through a dropping resistor 37 of, for instance, 27,000 ohms, balanced by resistor 33, also of, for instance, 27,000 ohms. Resistor 39 is of 70,000 ohms, for instance, and acts as a delay resistance. Capacitance 40 is an electrolytic condenser `and operates as a time delay device controlling the speed with which the biasing voltage is applied to grid 14 through resistance S5 of approximately 500,000 ohms. The time delay condenser 40 is controlled by variable resistance 41 of approximately 750,000 maximum ohms having a linear conguration. It will be observed that both resistor 41 and capacitance t0 are grounded at one side. The fade out time may be controlled by setting resistor 41 at a desired value. Approximately 5 seconds of fade in time has been found most pleasing.

In operation, when switch 13 is opened, the microphone is ready for operation. A conventional amplifier stage 42 is fed through lead 43 through resistance 44 which is a low level resistor filtering noise out of the amplification stage. Resistance 4S has a high ohmic value so that the microphone is suitably energizable from ground at 46 and prevents a condenser charging er'ect.

Condenser 47 is of the electrolytic type. lt provides a slowing down effect to the relay action and at the same time reduces relay induction. Resistor 48 is merely a dropping voltage resistor.

In the event that the sound system is to be employed in the conventional manner, that is, without the fade-in or `fade-out setup, control resisto-r 41 is turned to the off position, i.e., to ground and switch 49 is closed to make connection to ground at 50. Resistor 51 is merely a switch clicking filter. Switch 18 then becomes the means for snorting microphone 19 to ground at 50, thereby turning the microphone on or off, while grid 14 is biased in the off position.

The microphone amplifier stage 42 supplies amplified audio signal through lead 52 to grid S3 which is associated with plate 512 of mixer tube 15. Plate 54 provides a signal into the circuitry for the driver stage -along a common lead shared with the other plate 16 in the mixer tube.

In operation, it has been discovered that when resistance t1 is set to fade-out the music in one second as switch 18 is opened, the fade-back time for the music is 5 seconds as switch 13 is closed again. In other words, a preferred form of operation is to have the fade-back time for the music be approximately live times as slow as the fade-out time.

The foregoing is considered as illustrative only of the principles of the invention. Further, since numerous modifications and changes will readily occur to those skilled in the art, it is not desired to limit the invention to the exact construction and operation shown and described, -and accordingly all suitable modifications and equivalents may be resorted to, falling within the scope of the invention as claimed.

What is claimed as new is as follows:

1. An audio selective fading system comprising a i rst audio signal source, a second audio signal source, said second audio signal source being a microphone, means for feeding said iirst signal source to -a lfirst grid of a mixer thermionic tube the plate voltage thereof supplying energy to a driver, an amplifier connecting said second audio signal source and a second grid of said mixer thermionic tube, a source of negative biasing voltage connected to said iirst grid to bias said iirst grid to an ot position, a relay operated switch when closed capable of grounding said negative biasing voltage, a relay operated switch connected to the output of the microphone when closed capable of grounding said microphone.

2. An audio selective fading system comprising a iirst audio signal source, a second audio signal source, said second audio signal source being a microphone, means for feeding said first signal source to a first grid of a mixer therrnionic tube the plate voltage thereof supplying energy to a driver, an amplifier connecting said second audio signal source and a Second grid of said 4mixer thermionic tube, a source of negative biasing voltage connected to said rst grid to bias said first grid to an off position, a relay operated switch when closed capable of grounding said negative biasing voltage, a relay operated switch connected to the output of the microphone when closed capable of grounding said microphone, a time delay means adapted to cooperate with said negative biasing voltage to permit a gradual increase of biasing negative Voltage to the said first grid as the switch is opened.

3, The audio selective fading system of claim 2 wherein the time delay means includes an electrolytic condenser in cooperative arrangement with a variable energy level whereby the time delay period may be controlled.

4. The audio system of claim 3 wherein the variable energy level is accomplished by means of a variable resistance.

References Cited in the le of this patent UNITED STATES PATENTS 2,646,472 Rockwell July 2l, 1953 2,676,272 Byrd et al. Apr. 20, 1954 2,694,749 Hardy Nov. 16, 1954 

